During longitudinal seam-structure assembly the shells in the region of overlap are moved together over lining-up drill holes and are fastened. Subsequently the pilot drill holes are transferred. After drilling, the shells are moved apart and the burrs are removed from the drill holes. Thereafter sealant is applied and the shells are again moved together and are tacked.
The drill holes are then drilled open to their final dimensions and then countersunk and riveted. This requires considerable labour as a result of the placement of pop rivets and as a result of pilot drilling, drilling the pilot holes open and countersinking.
As an alternative to this manual method of the longitudinal seam-structure assembly a semi-automatic method can be used. In this method the shells, instead of being tacked, are screwed to jigs. On the rails of the drilling jig the so called LBOS-drilling unit (longitudinal-seam drilling system, manually positioned automatic drill feed unit with lubricant metering and suction removal for AL/AL and AL/titanium, with fastening in a drilling jig with rail guide in x and y directions) is installed, and all remaining drill holes are automatically drilled to final dimensions.
Subsequently, the shells are riveted. The provision of drilling jigs and a drilling system requires very considerable expenditure.